A vehicle's power assisted steering is a feature that is expected by many consumers and is provided in almost every passenger vehicle. Consumers have become accustomed to the failure modes of traditional Hydraulic Power Assist Steering (HPAS) insofar that typical failure modes are noticeable by the driver. HPAS failure modes typically comprise noise, leaks, and reduced and/or loss of power steering assist. Typically, a loss of power steering assist will be predicated by a leak or noise or both.
More recently, traditional HPAS systems are being replaced with Electric Power Assist Steering (EPAS) as the market demands advantages only a microprocessor controlled steering system can provide. EPAS systems show advances in features and quality. An EPAS system can monitor the state of the system many times per second (e.g., hundreds or thousands of times a second). Upon a detection of a problem, the system can act and bring the steering system to a safe state.
Shortcomings of existing systems include that the safe state is commonly a removal of the power steering assist feature itself, and typically without any other symptoms prior to the removal. This can be quite annoying and startling to the driver. Moreover, when analyzing the failure rates of the power assisted steering systems it is common to see a drastic increase of loss of assist failures when a vehicle platform migrates from a hydraulic to electric power.